| Popis: |
Introduction: It is unknown which factors regulate intracranial pressure (ICP) during body position changes in organisms with stenosis or obstruction inside of cerebrospinal fluid (CSF) space. To explore this problem a new ICP regulation hypothesis is proposed. According to our new hypothesis, the CSF pressure depends on the laws of fluid mechanics and on the anatomical characteristics inside the cranial and spinal space, and not, as is today generally believed, on CSF secretion, circulation and absorption. Material and methods: The volume and pressure changes in the newly developed CSF model, which by its anatomical dimensions and basic biophysical features imitates the craniospinal system in rabbits and cats, are compared to those obtained on animals with and without the blockade of craniospinal communication in horizontal and upright body position. Results:In upright position, a long lasting appearance of negative CSF pressure inside the cranium without changes in the blood and CSF volume was observed in animals with normal craniospinal communication. CSF pressure gradients change depending on the body position, but observed gradients do not enable unidirectional CSF circulation. In animals with cervical stenosis there is no appearance of negative ICP in upright position, on the contrary, this pressure is positive, which is in accordance with the theoretical consideration related to fluid mechanics. Similar intracranial pressure changes were observed on rabbits. Conclusions: Negative (subatmospheric) ICP inside the cranium in the upright position is not a transitory observed appearance, but a physiological state of the CSF pressure. Cerebral perfusion pressure is significantly higher in the upright position than it was previously supposed, which is a very important evolutionary adjustment. |
